Support for a pendant type luminaire



Oct. 6, 1959 R. w. HEINZEN 2,907,543

SUPPORT FOR A PENDANT TYPE LUMINAIRE Filed Aug. 15, 1955 3 Sheets-Sheet 1 IN VEN TOR.

Ruth M/ Heinzen BY flM f (Km fittorne y Oct. 6, 1959 R. W. HEINZEN SUPPORT FOR A PEND ANT TYPE LUMINAIRE Filed Aug. 15. 1955 a Sheets-Sheet 2' IZ'fiZumLnum \i Bracket Per Fig. g Q Q 760 s s Q 120 \l N I 12 SteeZ Brae/Ya:

Per F23 5. i 60 1 I/ertc'cal Deflection Ln /nc/zes fig. 4

INVENTOR.

Ruth I/M Henzen BY Wttorng Oct. 6, 1959 R. w. HElNZEN 2,907,543

SUPPORT FOR A PENDANT TYPE LUMINAIRE Filed Aug. 15, 1955 3 Sheets-Sheet 3 IN V EN TOR.

Rut/z W Hecrzzerz SUPPORT FOR A PENDANT TYPE LUMINAIRE Ruth W. Heinzen, Milwaukee, Wis., assignor to McGraw- Edison Company, a corporation of Delaware Application August is, 1955, Serial No. 528,394

3 Claims. 01. 248-221 The present invention relates to supporting brackets, and particularly relates to brackets of the upsweeptype adapted to support a pendant load, such as a street light or highway luminaire, from the terminal end thereof.

In the field of street lighting, there has been an increased tendency over recent years to provide support brackets of relatively extended length. This is especially true for installations adjacent roadways which extend past urban areas, requiring the supporting pole or standard to be spaced a considerable distance laterally of the road. For safety reasons the pole may notbe mounted on the shoulder of theroad, and very often it must be mounted even farther from the road because of a drainage ditch being provided adjacent the shoulder. In many instances, in order to mount a pole on firm ground laterally adjacent a road having both a shoulder and a drainage ditch, the support bracket extending laterally of the pole may be even as much as 20 ft. in length from the pole end to the terminal end.

Positioning of poles on boulevard dividing strips and where spreading trees may obscure projected illumination, also requires extended length'mast arm portions of the bracket. Obviously, the extended length subjects the bracket and the pole to considerable stress and strain even under normal weather conditions.

Wind loading has become a decided factor in strength requirements of street lighting components. In the past, luminaires were small and their supports were short. But today, with increased demands for quality lighting requiring large luminaires have resulted in the need for greater appreciation of wind loading.

In order to provide properly designed supports, two very important factors must be considered. These are pole space used and strength requirements. Naturally, both of these factors must be weighed and results accomplished with an aesthetically pleasing support. .Poles and other upright suport members are often used for multiple purposes.- For instance, it is quite normal for a pole to be used forsupporting primary lighting and other,

electrical circuits, inaddition to carrying telephone lines with multi-circuit installations. It is also considered to be good "practice to mount the street lightingluminaires at a considerable height, from the street; for instance, as much as 30 ft. In the past, with luminaire brackets of 12 ft inlength extending laterally from a pole, it was necessary to utilize as much as 4 ft. of polespace to mount a supporting guy member above the.

bracket pole plate. It will be readily apparent thatif the pole is to be used for multiple purposes, it is a decided advantage to provide a bracket requiring a minimum amount of pole height for adequate support.

L Certain basicstandards for bracket design have become accepted in the industry and include the following provisions:

(1) Less than deflection support lengths'when a 1O0 pound-vertical load is applied. This consideration allowslfor vice and luminaire loading. i

Lesa th an :2 degreesterminal deflectionfthrough Patented Oct. 6, 1959 the range to: 40 pounds vertical load. Thus, the light 0 support.

In addition, of 'course,-the supports should be attractive and easy to install.

The aesthetic considerations of a supporting bracket for a street lighting luminaire generally persuade a designer to provide a bracket of the upsweep type having a radius of curvature intermediate its ends. The main problem in curving a compression member, such'as a loaded mast arm, is the tendency for thatrnember to buckle under load in the direction of the curve. Another problem, introduced because of using a guy rod or'rods in tension is that the tension rod is not attached at the very end of the compression member. This introduces a tendency for the compression member to rotate'about the point where the rod is attached. The distance be tween the attachment point and the terminal point of the mast arm is necessary to permit proper mounting of a luminaire. 1

The present invention contemplates the use of a properly designed and located brace or strut inserted between the guy rod or rods and a curved'tcompression member, such as a street light mast arm, to cause a load applied on the support to produce on the compression member a deflecting and straightening force to counteract the buckling and rotation problems. In addition, the use of a spacer strut or brace results in a design which' acts to materially reduce the vertical space needed for mounting the bracket. Thus, more pole space is made'available for other equipment. The use of a spacer strut of proper design and location also adds considerably to the rigidity of the extended mast arm to provide a minimum lateral deflection at the terminal end. This is especially true when double guy rods are used.

It is an object of the present invention to provide a support bracket for mountingpendant loadspsuch as highway lighting luminaires, laterally spaced from an upright member, which bracket utilizes a minimum number of cooperating membersand requires. a minimum amount of pole heightfor securing the said partsthereto. "It is another object of the present invention to provide a supporting. bracket for highway, lighting luminaires which is aesthetic in appearance and of a design of maxi-: mum ultimate-strength, and having a minimum vertical and lateral deflection at its terminalend under loading conditions. a i v It is a further object of the present invention to provide. a luminaire support bracket of the upsweep type which w includes a tension guy member vertically spaced above length and'location relative to the supporting bracket assembly.

In the drawings:

Fig. 1 is a side elevation view of a supporting bracket constructed in accordance with the present invention,

; and shownm'ounted on a pole with a street light luminaire being mounted on the terminal end and illustrated in dot dashlines. I it Fig. 2 is .a top plan view of the bracket of Fig.1.- Fig. 3 is a sectional view taken on lines 33 of Fig. 1.

*Fig. -.4 isjagraphical representation of compositive fastened in place by means of nuts 2 2 threaded iiryes plotted fromyerticalloading data versus vertical deflection of supporting brackets of the prior art and of brackets embodying the present invention.

1 9. are, diagramtn-atic viewspoft brackets. and various representative portions thereof ill-ustra-tingcertain 5 aspec s to be considered in,v the proper dimension, and; lohe spacer strut or brace embodied in the pres .3 i ten :=1 r A preferred embodiment of the supportingbracket'is illustrated in ,Figs, 1, ,2 -and 3, wherein the bracket assemshownmounted on anupright woodpole orstandgird Theassemhly comprises an upsweep mastarmz attached to the pole 1 by means of a pole plate 3i. The pole, plate is here shown ,weldeddircctly to the-pole end of the mast arm, but may be of manyofseveral conyentional designs. The .poleplate 3 is .preferablymounted the .pole bvmeanslof .lag screws tand thru bolt-5. ast arnris preferably of conventional tubular. type f industry-accepteddimension forreceiving the .slipfitter portion of a luminaire 6. at the terminal end thereof. The luminaireisshown here. in dotted lines, and may-beef any of ,a vast multitude of varieties provided by several manufacturers. ,H Because of extended length of the mast arm 2, which may be as much as 20 ft. in certain cases,v tension memhers intheiorm of guy. rods ltliandlllare provided for added support. The guy rods. are fastened at the pole end by;means,of L-shaped brackets 12 and are threaded for adjustment by means of adjustment nuts 13 engaging the rods and respective brackets. The guy rods Hand 11 arefastened at their terminal endto the mast -arm-2- by means. of adjustable engagement with a guyrod support having apertures. therein for receiving the threaded terminal end of the guy rods and appropriate adjustment nuts 16. The guy rod support 14 may be-welded to the mast arm, 2, as shown, or mounted in any of several ways (not.;shown), as by means of a U-bol-t or the like; Thepresent invention contemplates the use of a guy rod braceorstrut intermediate the ends thereof, and being of particularproportion and location relative to the mast arm 2 and guy rods and 11. Although'double guy rods IO-and 11 are disclosed herein, it will be apparent as-the description proceeds that a single guy rod (not shown) may be used-for relatively shorter length mast arms without departing from the scope of this invention. In addition, it is often conventional practice, especially in the case of relatively extended length mast arms, to utilize whatis conventionally known as an A-frame construction of -themast-arm portion (not shown). 'This latter construction permits the mast arm pipe to be extended laterally of thepole-and supported from the pole by means of an'gularly relative angle irons welded thereto. his to be understood that the double guyrod construction isshown here for. illustrative purposes only, and that theteachings ofl-the present disclosure will serve equally well for any upsweep mast ar-m assembly in'cornpression when loaded and including one or more tensionmembers, such asguy rods, for additional-support. r

.In' thepresent embodiment, the guy rod strut or brace 20is formed from a stamping into ageneral L-shape as shown'inFigs. 2 and 3 and includes apertures for slidably, receiving the guy rod at the upper end thereof and al so in its lower'end to receive a conventional ll-bolt thereon As has previously been stated, the upsweep mast arm has a radius of curvature intermediate its, endsma'nly for. aesthetic purposes, which configuration' introduces two and; strength problems. inasmuch asthe ma i 4 d h r li da snd n xt buck e hfill. mpre siqnqby ppl g aloa i-isu h as the. Iuniinaire 6, at its terminal end. This is even .a;.gr;eaten problemthan if a straight m-ast arm werei t'o betprovi ded, as the curvature has alreadystarted the arm inadirection towards buckling. However, when a straight arm is 75 placed in compression, it may buckle in either direction if a great enough force is applied at its outer end.

The second problem arises because of the requirement of the point of attachment of the tension member, or members and the mast arm must be spaced inwardly from the terminal extremity in order to accommodate conventional luminaires. -When it is considered that many-luminaires weigh as much asforty pounds, andwthat the guy rod support 14 is positioned in many cases as much-asvl8 inches inwardly 0f the terminal end, there-is a considerable'rotative moment introduced, with the point of attachment acting. as a pivot.-v t The present invention contemplates the counteraction of the above introduced forcesby the provision of a properly proportioned and located guy rod strut or brace. The selection, dimension and location of the strut or brace 20 is determined by means of the following procedure}. .J. ..i i-; .Referrin-g to the diagram ofFig. 5, there is illustrated arconventional supporting bracket assembly 'u-tilizing a member-under compression, such-as the tubular mast arm-2 and a tension--memberormembers, such'as" the guy'rod 30. Both members are fastened to the pole in accordance with recognizedpractice, and for the-sake of convenience in description, it is assumed that the terminal ends of both members areattached at their extremity-t Thus, forthe moment, any tendency of the masta'rm to rotateabout the. point of attachment when a load P is applied, will not be-considered. ---As stated-previously, in a luminaire support of the construction shoWn in Fig.- 5, having an upsweep curved compressionmember, there will be a tendency to buckle at-the curved portion. I This compression mernben 'or mast arm z, can-be compared'to a column under-'com pression that hasalready been deflected beyond its critical point. Any compressive-load will cause it to deflect and ultimately buekledn the direction of the curve. Obviously,-this tendencytowards buckling will-be increased as the total length of the compression member is ex-' tended. 1

- The present invention contemplates the use of a spacer member, or guy rod brace 20 positioned between the guy rod or rods and-the mast arm as shown in Figs. 1,2, 3

and 6. It is'underst ood that struts have been placed between these members heretofore, but they have only been prescribed for increasing the rigidity of the entire assembly without consideration for proper location-and dimension to compensate for the tendencyof a curved compression member to buckle, and to correct for rotative momentaboutthe point of attachmentyas will hereinafter bedescribedu The tendency tobuckleunder load P is illustrated in Fig. 5 in the dotted line portion;

-An examination of the diagram' of Fig. 6 will illus trate the force diagram for the assembly under load V with the strut 20. being inserted between the tensionmember 10 andthe compression m'ember 2. The di agramof Fig. 6.. is representative ofthe forces imposed upon'the various members of the structure of'Figs. 1-3; The buckling tendency may be-cancelled by inserting the strut 20 between the guy and the mast arm, wherein'the strut is of such length and location that the upwardbuckling force F lof the arm will be balanced by a downward-force F which is caused -by the tendency of-- the guy rod to straighten under load. The maximum buckling tendency will occur at the mid point ofthe curved section between the guy attachment point and the point where curvature ceases. This has been found to'be' the preferred location for-the spacerstrut 20. The load P will cause the'curved arm to be compressed by a force designated-by the arrow F' whereas the tension rod is designatedby themember force on the guy symbol F i j I The-length L, the dimension H; A and the'radius of curvature R of the arin,-are determinedby other con'-' siderations including aesthetics and available pole height.

v.9 At any load P, the compressive force F and the tension force F can be determined by conventional procedure. The forces will be substantially equal and opposed to one another. As far as the dimension H is concerned, there is this to consider; in the case of a double guy rod construction as shown in Figs. 1-3, it has been found that when H is held to a minimum, the lateral deflection will 7 approach a minimum value for the guy construction V in Big. 7, .by treating the curved portion A of the mast arm 2 as a triangle,.with the forceF being applied along the sides thereof. The angle 06 may be determined from a layout similar to that of Fig. 7, or as follows: From an examination of the diagram of Fig. 7, it will be readily apparent that the angle a is approximately equal to t arc tan B/R. It will then be seen that the force F is equal to the compressive force F multiplied by the sine of theangle a.

Referring now to the diagram of Fig. 8, it will be seen that the guy rod, or tension member 10 maybe angularly proportioned to develop the compensating force F; as follows: Let F be equal to F It will then be seen that the angle [3 defined by the necessary height of the strut 20 may be determined from the equation: Sine fl=F /F The angle T will then be equal to 180-2B. After the angle T is determined, the length of the spacer strut necessary to maintain that angle may be found immediately by layout.

Although no particular attention has heretofore been considered in the present description relating to the strength of material consideration, it must be assumed that the guy rod or rods, mast arm and spacer materials are chosen of sufiicient strength to receive the necessary loads applied to them, in addition to accounting for a considerable factor of safety.

As stated heretofore, the above procedure was outlined with the assumption that the guy rod was to be attached at its outer extremity directly to a point on the mast arm vertically of the load P. However, in actual practice, there is a considerable free length of mast arm extending beyond this point for proper attachment of a luminaire. This may often be as much as 18 inches in a mast arm of the length of 12 ft. measured laterally from the pole. Referring to Fig. 9, it will be apparent that such attachment will result in a couple, tending to rotate the arm about the guy rod attachment point. Thisfree end dimension K provides a considerable factor which must be considered in the calculations to permit a proper design of spacer strut to compensate for both the tendency of the pipe to buckle and for the rotative moment introduced.

For purposes of calculation, the portion K of the arm between the spacer strut 20 and the point of load attachment may be treated as a lever with its fulcrum at the guy attachment point, as shown in'Fig. 10. The force F required to neutralize the moment at that point is:

The angle T on the guy rod must then be modified to permit F to equalF plus F It will be obvious that in normal practice, the calculations will consider the IQ- tative force F immediately on determination of the angle T. The present procedure has been outlined as above for the sake of clarity in discussion.

Another factor that must be considered in determining whether double guy rods should be used rather than a single guy rod, is that there is some instability introduced by heavy loads due to the tendency of the strut 20 to rotate, which must be" opposed by the torsional strength of the mast arm. If double gu-y rods are used with considerable spacing between each other of the spacer strut and pole, then they will counteract any mast arm torsion under verticalloading, and tend to reinforce the lateral strength by introducing a torsional component tothe pipe. I 1

It is interesting to note the relative strength and pole height considerations provided by the introduction ofthe properly designed and located spacer strut. Attention is now directed to the curves of Fig. 4, wherein the calculations for the curves were determined from tests on substantially comparable designs of a supporting bracket, such as the preferred embodiment shown in Figs. 1, 2 and 3, and of a conventional bracket, diagrammatically illustrated in Fig. 9. In addition, it is evenof more worthy note to observe that the curve of the structure of the preferred embodiment was laid out from tests on an all aluminum mast arm, as compared to a steel mastzarm according to a diagram of Fig. 9.

ln making the tests, both structures were of a total mast arm length of 12 ft. The pole height H in the steel structure was 4 ft. as opposed to a height of 18 inches in the aluminumstructure. This is a considerable saving in, pole height; and perjmitsthe luminaires to be mounted at optimum height above street level for proper illumination and also provides additional space for poles designed for multiple use. A very graphic difference will become immediately apparent from Fig. 4, when it is observed that a pendant load of only pounds deflected the steel structure 5 inches when no brace or strut was used, whereas the 5 inch deflection in the aluminum structure was obtained only after applying a load of 240 pounds.

A close observation of the structure of Figs. 1 and 2 will reveal that, in the present case, the brace 20 is positioned slightly inwardly of the center of the curved portion of the mast arm 2. In commercial practice, luminaires are generally provided with mast arm slipfitters of only two different diameters. It will be obvious that the procedure outlined above relates to optimum practice for a particular length mast arm, and that relatively shorter mast arms of the same diameter will permit shifting inwardly of the strut 20 for ease in manufacture and assembly without departing from desired strength characteristics of the novel bracket assembly.

It will be apparent that an improved supporting bracket has been provided for supporting pendant loads laterally spaced from a vertical support, which bracket includes a guy rod spacer of proper dimension and location relative to the various support members to provide a minimum amount of pole space for mounting and which further provides a maximum degree of rigidity in both vertical and lateral deflection characteristics.

I claim:

1. A support. for a pendant type luminaire in laterally spaced relation to an upright member comprising in combination, a mast arm normally under compression and subject to unbalanced buckling forces attached at one end to said upright member by means of a pole plate and having a free outer end for supporting a luminaire, an elongated tensioned guy member having first and second portions in angularly disposed relationship to each other and having a point of confluence intermediate the ends of said guy member, said guy member being attached at one of its ends to said upright member and at the other of its ends to said mast arm, strut means attached to said mast arm intermediate the ends thereof and engaging said guy member at said point of confluence of said first and second angularly disposed portions, said point of confluence being in vertically upwardly spaced relation to the point of attachment of said one end of said guy member to said upright member whereby said strut means is placed under compression for counteracting said forces tending to buckle said mast arm.

2. A support for a pendant type luminaire in later- :ally spaced relation toan upright member-comprising in combinationyan elongated curvilinear mast arm normally undercompression and subject to unbalanced buckling forces, said mast arm being attached toa .lower end to said upright member by means of a pole plate and rising generally upwardly to a free outer end forsupporting a luminaire, an elongated tensioned 'guy member ha vingfirst and second portions in angularly disposed relationship to each other and having a point of confluence intermediate the ends of said guy memher, said guy member being attached at one end to said upright member in vertically spaced relationship to said pole plate andat the other end 'to said mast arm in proximity to said free outer end, strut means attached to-said mast arm intermediate the ends thereof and engagingsaid guymember at said point of confluence of said first and-second angularly disposed portions,'said point ofconfluence being in vertically spaced relation to the point of attachment of said one end of said guy member to said upright member whereby said strut means is placed under compression for counteracting said forces tending tobuckle said curvilinear mast arm.

3. A; support for a pendant type luminaire in laterally spaced relation to an upright member comprising in combination, a mast arm normally under compression and subject to unbalanced buckling forces attached at one ,end to said upright member by means of a pole plateand having a free outer end for supporting 'a luminaire, a pair of elongated tensione'd, guy members each having first and second portions in angularly disposed relationship to each other and each having a point of confluence intermediate the ends of said guy members,

' each of said guy members being attached at one. of 'its ends to said upright member and at the other of its ends to said mast arm, a strut member attached to "said mast arm intermediate the ends thereof and engaging each of said guy members at each of said points of confluence of said first and second angularly disposed portions, said 7 points of confluence'being in vertically spaced relation to the point of attachment of each of said one ends of.

said guy members to said upright member whereby said strut member is placed under compression for "counteracting said torcestending to buckle said mast arm.

References'Cited in the file ofthis patent UNITED STATES PATENTS 636,327 Fletcher Nov. 7, 2,653,782 Pfafi Sept. 29, 1953 2,731,227 Anderson Ian. 17, 1956 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 2,907,543 October 6, 1959 Ruth W. Heinzen It is hereby certified that error appears in the-printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column '7, line 5, for "attached to" read attached a Signed and sealed this 5th day of April 1960.

(SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner of Patents 

